Which type of medication to use initially for hypertension has been the subject of several large studies and resulting national guidelines.The fundamental goal of treatment should be the prevention of the important "endpoints" of hypertension such as heart attack, stroke and heart failure. Several classes of medications are effective in reducing blood pressure. However, these classes differ in side effect profiles, ability to prevent endpoints, and cost. The choice of more expensive agents, where cheaper ones would be equally effective, may have negative impacts on national healthcare budgets.[2]

In the United States, the JNC7 (The Seventh Report of the Joint National Committee on Prevention of Detection, Evaluation and Treatment of High Blood Pressure) recommends starting with a thiazide diuretic if single therapy is being initiated and another medication is not indicated.[3]
This is based on a slightly better outcome for chlortalidone in the ALLHAT study versus other anti-hypertensives and because thiazide diuretics are relatively cheap.[4]
A subsequent smaller study (ANBP2) published after the JNC7 did not show this small difference in outcome and actually showed a slightly better outcome for ACE-inhibitors in older male patients.[5]

Despite thiazides being cheap, effective, and recommended as the best first-line drug for hypertension by many experts, they are not prescribed as often as some newer drugs. Arguably, this is because they are off-patent and thus rarely promoted by the drug industry.[6]

Only the thiazide and thiazide-like diuretics have good evidence of beneficial effects on important endpoints of hypertension, and hence, should usually be the 1st choice when selecting a diuretic to treat hypertension. The reason why thiazides-type diuretics are better than the others is (at least in part) thought to be because of their vasodilating properties.[How to reference and link to summary or text]

Although the diuretic effect of thiazides may be apparent shortly after administration, it takes longer (weeks of treatment) for the full anti-hypertensive effect to develop.

Although beta blockers lower blood pressure, they do not have as positive a benefit on endpoints as some other antihypertensives.[9]
In particular, atenolol seems to be less useful in hypertension than several other agents.[10]
However, beta blockers have an important role in the prevention of heart attack in people who have already had a heart attack.[11]

Despite lowering blood pressure, alpha blockers have significantly poorer endpoint outcomes than other antihypertensives, and are no longer recommended as a first-line choice in the treatment of hypertension.[12]
However, they may be useful for some men with symptoms of prostate disease.

Central alpha agonists lower blood pressure by stimulating alpha-receptors in the brain which open peripheral arteries easing blood flow. Central alpha agonists, such as clonidine, are usually prescribed when all other anti-hypertensive medications have failed. For treating hypertension, these drugs are usually administered in combination with a diuretic.

Blood pressure vaccinations are being trialed and may become a treatment option for high blood pressure in the future. Research on the vaccine CYT006-AngQb published in The Lancet on the 8 March 2008 titled, “Vaccination against high blood pressure: a new strategy” showed patients experienced a drop in systolic and diastolic blood pressure after taking the vaccine.
Effective blood pressure vaccines would assist those people who forget to take their medication. It would also help those who stop taking their medication due to side effects or falsely believing they don't need them anymore once their blood pressure is lowered.[13]

The choice between the drugs is to a large degree determined by the characteristics of the patient being prescribed for, the drugs' side-effects, and cost. For example, asthmatics have been reported to have worsening symptoms when using beta blockers. Most drugs have other uses; sometimes the presence of other symptoms can warrant the use of one particular antihypertensive (such as beta blockers in case of tremor and nervousness, and alpha blockers in case of benign prostatic hyperplasia). The JNC 7 report outlines compelling reasons to choose one drug over the others for certain individual patients.[3]